The present invention relates to a laminate having excellent gas impermeability, and more particularly to a laminate having improved flex crack resistance, drawability and heat moldability as well as excellent gas impermeability.
A hydrolyzed ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH copolymer") is thermoplastic and is excellent in transparency, antistatic property, oil resistance, solvent resistance, gas impermeability and odor retaining property. However, the EVOH copolymer is poor in impact resistance, flex crack resistance, drawability, heat moldability, gas impermeability under high humidity, and the like.
Therefore, it is proposed in Japanese Examined Patent Publication No. 6192/1974 that one side of the EVOH copolymer film is provided with a low density polyethylene layer and the other side is provided with a film such as polypropylene, nylon or polyester film, thereby improving the defects of EVOH copolymer such as poor impact strength, heat moldability and moisture resistance with maintaining the advantages of EVOH copolymer such as excellent gas impermeability, odor retaining property and property for preventing discoloration of foods.
On the other hand, in order to improve the impact resistance and drawability of the EVOH copolymer without impairing remarkably advantages thereof, Japanese Examined Patent Publication No. 24277/1969 proposes to blend a polyamide with the EVOH copolymer or Japanese Unexamined Patent Publication No. 139733/1985 or No. 161453/1985 proposes to blend a polyamide-polyether block copolymer with the EVOH copolymer.
However, in the laminating method in Japanese Examined Patent Publication No. 6192/1974, the flex crack resistance of the laminated film having EVOH copolymer layer as a gas impermeable layer is unsatisfactory. Therefore, when flexing the laminated film, it is easy to generate pin holes in the EVOH copolymer layer, and on the other hand, in thermoforming such as deep drawing, it is hard to draw the EVOH copolymer layer evenly, thereby impairing the gas impermeability, thus resulting in remarkable limitation of the use of the laminated film as wrapping or packaging materials.
On the other hand, when blending the polyamide with the EVOH copolymer, the impact resistance and drawability can be improved, but there is a defect that gas impermeability is greatly lowered. Also, the EVOH copolymer blended with the polyamide-polyether block copolymer has the improved flex crack resistance and drawability as well as excellent gas impermeability, but laminated films prepared therefrom is unsatisfactory in flex crack resistance or drawability.
An object of the present invention is to provide a laminate having improved flex crack resistance, drawability and heat moldability as well as excellent gas impermeability.
This and the other objects of the present invention will become apparent from the following description.